WIRE
Wire Size Calculator (sq mm) for House Wiring
Find the copper wire size in sq mm for a load and distance, single or three phase, checked for current, voltage drop and the usual minimum per circuit, with the MCB.
Assumptions used EDIT ▾
3% is a common limit.
Ratings are conservative values for PVC-insulated copper house wire, two wires in a conduit; wires bunched together, hot roofs or long runs need a bigger size. The wire must carry the current plus 25% and keep voltage drop under the limit. Always follow the wire maker's rating table and have a licensed electrician check the circuit.
COPPER WIRE
2.5sq mm
Chosen for the usual minimum for this circuit
- CurrentWire rating 18 A
- 8.7 A
- Voltage drop1.1% of 230 V
- 2.5 V
- MCBProtects the wire; never larger than its rating
- 10 A
How it’s calculated
I = W ÷ (230 × pf); choose the smallest wire rated ≥ I × 1.25 with voltage drop 2 × L × I × R ≤ 3%
Example: 2,000 W geyser, 15 m: I = 8.7 A; 1.5 sq mm would carry it with 1.8% drop, but a geyser circuit is usually at least 2.5 sq mm, with a 10 A MCB.
Questions
What size wire for lights, sockets, AC and geyser?+
A common practice in Indian homes: 1.5 sq mm for lights and fans, 2.5 sq mm for 16 A power sockets and geysers, 4 sq mm for air conditioners. Long runs may need the next size up.
Why does the length of the wire matter?+
Longer wire has more resistance, so the voltage at the far end drops. Too much drop makes motors run hot and lights dim; a thicker wire fixes it.
Is the MCB supposed to protect the appliance?+
The MCB protects the wire. It must never be rated higher than the wire can safely carry.
Can I use aluminium wire instead?+
Aluminium carries less current than copper of the same size and its joints loosen over time. For house wiring, copper is the safe choice.
Estimates for planning, based on the assumptions shown. They are not a guarantee of quantities or professional engineering advice; check critical work with a qualified professional.